PC-417 lift issue

[mascan42]

I have a BH650i with a PC-417 feed unit. Tray 3 is having trouble lifting if the tray is more than half full. It makes loud knocking noises and the stack drops slightly before continuing up. It never gets to the point where it codes out, but the customer is very concerned about it. I've already replaced the lift motor, and it had no effect. The coupling is part of the motor, so that's been replaced as well.

The trick is, if the tray is only slightly full, it can travel the further distance without issue because of the low weight. But OTOH, if the tray is filled almost to the top, it's also fine; the weight doesn't seem to matter because it doesn't have as far to travel. But at some point in between, it's both too heavy and has to travel too far, and thus I get loud thumping noises.

Any idea where I should be looking? There's no obvious issue with the lift cable, and I think the only gearing is in the braking system.

[Synthohol]

push the tray in during lift. ive seen the couplings slip under full tray weight. may be split coupling.
turn coupling by hand to see if all lift wires are even while lifting.
ive adjusted the "tray depth" to compensate if it is the coupling.
customers slam trays too hard and shifts the carriage so it dont make full contact.
good luck!

[mascan42]

push the tray in during lift. ive seen the couplings slip under full tray weight. may be split coupling.
turn coupling by hand to see if all lift wires are even while lifting.
ive adjusted the "tray depth" to compensate if it is the coupling.
customers slam trays too hard and shifts the carriage so it dont make full contact.
good luck!

I tried holding the tray in, and it made no difference. And like I said, the only coupling on this model is on the motor, which I already replaced.

[Synthohol]

can you remover tray 1 and 2 and watch it from the inside?
if one corner lags behind it can cause the tray to tilt and bind especially when full because the extra paper friction slowing and halting its ascend.
those cables are a PITA once the wires slip off the gear on to the shaft.
id take out the tray, remove the covers to expose the lift cables and turn the tray shaft by hand and watch the travel on all the wires under load.